The ATM is a standard transfer mode constituted by ITU-T (International Telecommunication Union—Telecommunication Standardization Sector), in which information is organized into information elements. Since each information element including the information from a certain user does not need to occur periodically, this transfer mode is asynchronous. ITU-T named this technology ATM technology in 1988 and recommended it as the information transfer mode of B-ISDN (Broad Integrate Service Digital Net). Because the ATM technology simplifies the switching process, eliminates unnecessary data checks, and adopts a fixed format of information element which is easy to be processed, the switching velocity of ATM is greatly higher than that of a conventional data network, such as X2.5, DDN (Digital Data Network) and frame relay networks.
The transmission links of ATM are divided into two levels: Virtual Path (VP) level and Virtual Channel (VC) level. In addition, for the data network with such a high speed, some effective supervisory mechanisms for service streams are adopted in ATM networks to make real-time supervision on online user data, so that the probability of network congestion is minimized. Different privileges are granted to different services. For example, the voice service has the highest real-time privilege while common data file transmission has the highest correctness privilege. The network assigns different network resources to different services according to different QoS (Quality of Service), so that different services can coexist in harmony and run efficiently. The service types of ATM includes: Constant Bit Rate (CBR), real-time Variable Bit Rate (rt-VBR), non-real-time Variable Bit Rate (nrt-VBR), Unspecified Bit Rate (UBR) and Available Bit Rate (ABR).
ATM broadband networks, constituted on the base of ATM switches, can provide narrowband and broadband information with an integrated and uniform transfer platform, which can satisfy the transmission of integrated services, and guarantee the QoS effectively. In other words, ATM is applicable not only to the burst services such as data information transmission, but also to the services of a higher real-time requirement, such as transmission of voice, video image and so on. In terms of adaptability of data transmission, an ATM network can be adapted for a low-velocity transmission, a high-velocity transmission, and a variable-velocity transmission. Therefore, ATM has a broad prospect of application and is worth active exploration and development.
Generally speaking, an ATM network consists of an access layer and a core layer. The access layer includes local ATM devices or sub-networks, and the core layer is a switching network. According to the need of network applications, the ATM devices can be configured into network topologies such as a chain, a tree, a star, a ring, and a reticulation. Different networking modes require different structures, as well as hardware, software and maintenance of ATM devices. Due to the particularity of the ATM technology, for example, the particularity of being based on virtual connections, the particularity of fixed-length packets switching and so on, ATM devices can bear different services including broadband services and narrowband services. However, if an ATM device is required to support all networking modes, it will be very complicated and expensive. In particular, if the network architecture needs to be modified after the networking mode of ATM devices is determined, there will be such problems as difficulty in software and hardware upgrading or modification, heavy burden of modifications on configuration data, long time interruption of services. Therefore, in ATM networks of the prior art, one type of ATM device usually supports only one or a few specific networking modes.
FIG. 1a to FIG. 1e are the schematics illustrating different network topology of a chain, a tree, a star, a ring and a reticulation, respectively, constituted by a plurality of ATM devices. Each node is an ATM device. For the chain networking, as shown in FIG. 1a, an end node provides one interface and an intermediate node provides two interfaces; nodes are connected pairwise by interfaces to constitute a chain network; the switch of an intermediate node switches the services passing this node from other nodes in addition to switching the services of this node.
For the star network, as shown in FIG. 1b, there is only one assembly node in the network, and except the assembly node, each of other nodes has only one interface respectively which is connected to one of the interfaces of the assembly node. All the service connections in the network need to be switched in the assembly node.
For the tree network, as shown in FIG. 1c, there are multiple assembly nodes in the network, and assembly nodes connect with each other by interfaces; all the service connections in the network need to be switched via one or multiple assembly nodes.
For the ring network, as shown in FIG. 1d, all the nodes in the network are connected in series, and the beginning node is connected with the ending node; the connection of any two nodes includes two paths which can backup each other. This network topology is of high survivability.
For the reticular network, as shown in FIG. 1e, there are multiple pairs of nodes which are connected with each other, and it is called an ideal reticular topology if all the nodes are directly connected with each other. The reticular architecture is not influenced by the problems of node bottleneck and invalidation, and there are multiple routes between two nodes so that it is highly reliable.
To meet the requirement of applications of the networking modes, complicated software and hardware have been designed so that various types of hardware interface and software interface are furnished in the network devices; the hardware interface and software interface are selected according to the type of networking in use. If the networking mode is changed, the software and the hardware need to be replaced or upgraded; alternatively, the networking is implemented directly via the interconnection of interfaces, i.e. by means of ATM switching network plus interfaces. ATM service devices for switching use are interconnected via the self-furnished interfaces; the network interfaces, i.e. the networking interfaces, and local user interfaces are managed uniformly.
In practical applications, however, according to the above networking solution, the devices cost a great deal, and are complicated in terms of design and maintenance, as well as in configuration with each other. The network architecture is difficult to change. In addition, large numbers of ports of the switching network have to be occupied, and services from other nodes by way of this node occupy the switching network resources of this node, which greatly confines the inter-connecting service between networks while sacrificing the switching capacity of local services of each node. Moreover, complicated configuration makes it easy to produce errors in butting and it is impossible to change the network architecture online. Under certain networking circumstances, such as ring networking, it is difficult to implement dynamic protection switching of ring network services.
The major reason is that an ATM network device has integrated all the function modules, binding functions associated with networking interface with functions of local switching so that services of the switching network and local services can not be processed separately while changes in networking have an impact on the functions of the entire device, resulting in an increasing complexity in implementation and maintenance and compromising the efficiency and reliability of the system.